package thired.class04_mergesort;

import com.zrrd.sort.MergeSort;

public class Class01_MergeSort {
    public static void mergeSort(int[] nums){
        if(nums == null || nums.length < 2){
            return;
        }
         process(nums,0,nums.length - 1);
    }
    public static void process(int[] nums,int l,int r){
        if(l==r){
            return;
        }
        int mid = l + (r - l >> 1);
        process(nums,l,mid);
        process(nums,mid+1,r);
        merge(nums,l,mid,r);
    }
    public static void merge(int[] nums,int l,int mid,int r){
        int[] help = new int[r-l+1];
        int i = 0;
        int p1 = l;
        int p2 = mid + 1;
        while(p1 <= mid && p2 <= r){
            help[i++] = nums[p1] <= nums[p2] ? nums[p1++] : nums[p2++];
        }
        while(p1 <= mid){
            help[i++] = nums[p1++];
        }
        while (p2 <= r){
            help[i++] = nums[p2++];
        }
        for (int j = l; j <= r; j++) {
            nums[j] = help[j - l];
        }
    }
    // 非递归方法实现
    public static void mergeSort2(int[] nums) {
      if(nums == null || nums.length < 2){
          return;
      }
      //步长
      int sizeStep = 1;
      while (sizeStep <= nums.length){
          int l = 0;
          while(l < nums.length){
              if(sizeStep >= nums.length-l){
                  break;
              }
              int mid = l + sizeStep - 1;
              int r = Math.min( mid + sizeStep,nums.length - 1);
              merge(nums,l,mid,r);
              l = r + 1;
          }
//          if (sizeStep > nums.length / 2) {
//              break;
//          }
          sizeStep <<= 1;
      }
    }

    // for test
    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
        }
        return arr;
    }

    // for test
    public static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    // for test
    public static boolean isEqual(int[] arr1, int[] arr2) {
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
            return false;
        }
        if (arr1 == null && arr2 == null) {
            return true;
        }
        if (arr1.length != arr2.length) {
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i]) {
                return false;
            }
        }
        return true;
    }

    // for test
    public static void printArray(int[] arr) {
        if (arr == null) {
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    // for test
    public static void main(String[] args) {
        int testTime = 500000;
        int maxSize = 100;
        int maxValue = 100;
        System.out.println("测试开始");
        for (int i = 0; i < testTime; i++) {
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);
            mergeSort(arr1);
            mergeSort2(arr2);
            if (!isEqual(arr1, arr2)) {
                System.out.println("出错了！");
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println("测试结束");
    }
}
